Wolbachiaas a possible means of driving genes into populations

Abstract

SummaryCytoplasmic incompatibility consists of sterility in cross matings, the crossing type being maternally inherited. It can be explained by the action ofWolbachiasymbionts which are transmitted through the egg cytoplasm and leave an imprint on the sperm which prevents it fertilizing unless it is ‘rescued’ by the action of the same type ofWolbachiain the egg. Thus matings between infected males and uninfected females are sterile, but the reciprocal matings are fertile. Hence uninfected females are at risk of failing to transmit their uninfected cytoplasm if they cross mate, but infected females are at no such risk. Therefore natural selection favours the infected state and in two wild insect populations the infection has been observed spreading. If a gene for inability to transmit malaria could be introduced intoWolbachiaand if this could be introduced intoAnopheles(where these symbionts appear not to occur naturally), release of a limited number of such insects should trigger a process of displacement of malaria vectors, by the non-vector type. A simple model is used to demonstrate the limitations to this process which would be introduced by immigration.